Carriers or operators of high bandwidth networks, such as optical networks, typically sell network access to their customers, which often include telephone companies or other telecommunications service providers. For example, an operator of an optical network segment extending between two major cities may receive a number of communications signals or channels from a number of respective customers at an originating city, which are then multiplexed or combined into a single higher-speed optical communications signal. The higher-speed signal is then relayed to the destination city, where it is then demultiplexed or split apart into its component signals, which are then separately provided to the respective customers' facilities in the destination city.
Each communications signal initially provided by a customer of the network operator typically includes a payload portion in which the actual “live” communications traffic is stored, and further includes a transport overhead portion which is used by the customer for various purposes, including monitoring the occurrence of transmission errors that may arise on the customer's own communications equipment and facilities.
However, as each customer's communications signal is carried over the network operator's optical network segment extending between the two cities, it generally passes through a number of different network elements at which it is necessary for the network operator's equipment to over-write the customer's transport overhead data, in order for the network operator to monitor the occurrence of errors on the optical network segment.
Accordingly, when the communications signal is relayed to the customer at the destination city, much of the customers transport overhead information has been destroyed. This may interfere with or destroy the ability of the customer to monitor aspects of its own facilities, such as the occurrence of errors on the customers equipment in the vicinity of the originating city, for example.
Accordingly, it would be desirable, from the point of view of some such customers, for the network operator to be able to provide a “clear channel” across the network segment, or in other words, for the network operator to pass transport overhead information to the customer at the destination city in such a way that the customer's ability to monitor the occurrence of errors on its own facilities would not be affected by anything that may have occurred over the operator's network segment, as if the network segment did not exist. One approach to a similar problem involves providing special dedicated facilities on the network segment, including a transparent multiplexer or combiner for example, along with special line facilities that preserve portions of the customer's incoming overhead information for reconstruction at the destination, so that the preserved overhead is effectively passed through the network segment transparently. Disadvantageously, however, such dedicated facilities are not capable of combining a mixture of transparent and non-transparent channels into a single optical signal, with the result that such facilities are useful only in circumstances where all of the customers whose signals are to be combined together desire transparent access to the network segment. In addition, if the individual signals that have been multiplexed into the single optical signal are not all destined for the same network node or location, it is not possible for these dedicated facilities to perform the usual seamless extraction of the individual signal at the intervening node at which the individual signal is to be dropped off. Rather, the entire signal must be demultiplexed in order to extract the individual signal that is to be dropped off, and the individual signals that are destined for subsequent network locations must be re-multiplexed or combined back into a new optical signal. This results in significantly increased equipment costs, as additional demultiplexers and re-multiplexers must be provided at any such intervening network node for signals that are merely passing through the network node. Accordingly, these dedicated facilities are not well-suited to accommodating the differing needs of different customers, and result in significantly increased equipment costs for network operators.
Accordingly, there is a need for an improved way of providing clear channel access.